diff --git a/src/api/controllers/map.controller.ts b/src/api/controllers/map.controller.ts
index fbb89a7..b90fd08 100644
--- a/src/api/controllers/map.controller.ts
+++ b/src/api/controllers/map.controller.ts
@@ -186,13 +186,16 @@ export class MapController {
         return;
       }
 
-      await this.discoveryService.clearCache(url);
+      const keysCleared = await this.discoveryService.clearCache(url);
 
-      logger.info('Discovery cache cleared', { url });
+      logger.info('Discovery cache cleared', { url, keysCleared });
 
       res.status(200).json({
         success: true,
-        message: 'Cache cleared successfully'
+        keysCleared,
+        message: keysCleared > 0
+          ? `Cleared ${keysCleared} cached ${keysCleared === 1 ? 'entry' : 'entries'} for this URL`
+          : 'No cached entries found for this URL'
       });
 
     } catch (error) {
diff --git a/src/services/url-discovery.service.ts b/src/services/url-discovery.service.ts
index 630cfc1..aa4c4e0 100644
--- a/src/services/url-discovery.service.ts
+++ b/src/services/url-discovery.service.ts
@@ -1069,10 +1069,13 @@ export class URLDiscoveryService {
     }
   }
 
-  /** Registrable base domain from a hostname (naive last-two-labels heuristic). */
+  /**
+   * Registrable base domain from a hostname. Delegates to the same helper the
+   * result filter uses (URLValidationUtils.registrableDomain), so the subdomains
+   * this discovers and the subdomains the filter keeps can never disagree.
+   */
   private baseDomainOf(hostname: string): string {
-    const labels = hostname.split('.').filter(Boolean);
-    return labels.length > 2 ? labels.slice(-2).join('.') : hostname;
+    return URLValidationUtils.registrableDomain(hostname);
   }
 
   /**
@@ -1484,6 +1487,22 @@ export class URLDiscoveryService {
   /**
    * Generate cache key for discovery options
    */
+  /**
+   * A stable per-URL token embedded in the cache key so `clearCache(url)` can
+   * find every cached variant (different maxUrls/options) for one URL. Normalized
+   * (scheme + lowercased host + path, no trailing slash) so trivial differences
+   * like a trailing slash still match.
+   */
+  private urlKeyToken(url: string): string {
+    try {
+      const u = new URL(url);
+      const path = u.pathname.replace(/\/+$/, '');
+      return encodeURIComponent(`${u.protocol}//${u.hostname.toLowerCase()}${path}`);
+    } catch {
+      return encodeURIComponent(url ?? '');
+    }
+  }
+
   private generateCacheKey(options: DiscoveryOptions): string {
     const keyData = {
       url: options.url,
@@ -1498,7 +1517,8 @@ export class URLDiscoveryService {
 
     const keyString = JSON.stringify(keyData);
     const hash = require('crypto').createHash('sha256').update(keyString).digest('hex');
-    return `${this.cachePrefix}:${hash}`;
+    // The URL token makes keys clearable by URL; the hash keeps per-option variants distinct.
+    return `${this.cachePrefix}:${this.urlKeyToken(options.url)}:${hash}`;
   }
 
   /**
@@ -1537,25 +1557,31 @@ export class URLDiscoveryService {
   }
 
   /**
-   * Clear discovery cache for a specific URL
+   * Clear every cached discovery variant for a specific URL. Returns the number
+   * of cache entries removed.
+   *
+   * Cache keys are `url-discovery:<urlToken>:<optionsHash>`. The previous code
+   * matched keys with `.includes(encodeURIComponent(url))`, but the URL never
+   * appeared in the key (it was folded into the hash), so this always matched
+   * nothing and silently cleared zero entries.
    */
-  async clearCache(url: string): Promise<void> {
+  async clearCache(url: string): Promise<number> {
     try {
-      const pattern = `${this.cachePrefix}:*`;
-      const keys = await redisClient.keys(pattern);
-
-      // Filter keys that contain the URL
-      const urlKeys = keys.filter(key => key.includes(encodeURIComponent(url)));
+      const keys = await redisClient.keys(`${this.cachePrefix}:*`);
+      const prefix = `${this.cachePrefix}:${this.urlKeyToken(url)}:`;
+      const urlKeys = keys.filter(key => key.startsWith(prefix));
 
       if (urlKeys.length > 0) {
         await redisClient.del(...urlKeys);
-        logger.info('Cleared discovery cache', { url, keysCleared: urlKeys.length });
       }
+      logger.info('Cleared discovery cache', { url, keysCleared: urlKeys.length });
+      return urlKeys.length;
     } catch (error) {
       logger.warn('Failed to clear discovery cache', {
         url,
         error: (error as Error).message
       });
+      throw error;
     }
   }
 
diff --git a/src/utils/url-validation.subdomain.spec.ts b/src/utils/url-validation.subdomain.spec.ts
new file mode 100644
index 0000000..5a2897c
--- /dev/null
+++ b/src/utils/url-validation.subdomain.spec.ts
@@ -0,0 +1,49 @@
+import { URLValidationUtils } from './url-validation.utils';
+
+describe('URLValidationUtils.registrableDomain', () => {
+  const cases: [string, string][] = [
+    ['www.sonarsource.com', 'sonarsource.com'],
+    ['docs.sonarsource.com', 'sonarsource.com'],
+    ['sonarsource.com', 'sonarsource.com'],
+    ['a.b.c.sonarsource.com', 'sonarsource.com'],
+    ['fuel-finder.uk', 'fuel-finder.uk'],
+    ['www.example.co.uk', 'example.co.uk'],
+    ['docs.example.co.uk', 'example.co.uk'],
+    ['shop.example.com.au', 'example.com.au'],
+    ['localhost', 'localhost'],
+    ['192.168.0.1', '192.168.0.1'],
+    ['WWW.SonarSource.COM', 'sonarsource.com'],
+  ];
+  it.each(cases)('%s -> %s', (host, expected) => {
+    expect(URLValidationUtils.registrableDomain(host)).toBe(expected);
+  });
+});
+
+describe('URLValidationUtils.matchesDomain (the includeSubdomains fix)', () => {
+  const seed = 'https://www.sonarsource.com';
+
+  it('keeps sibling subdomains when includeSubdomains is true (regression)', () => {
+    // This is the exact bug: a www. seed used to DROP docs./blog./community.
+    expect(URLValidationUtils.matchesDomain('https://docs.sonarsource.com/x', seed, true)).toBe(true);
+    expect(URLValidationUtils.matchesDomain('https://blog.sonarsource.com/y', seed, true)).toBe(true);
+    expect(URLValidationUtils.matchesDomain('https://www.sonarsource.com/z', seed, true)).toBe(true);
+    expect(URLValidationUtils.matchesDomain('https://sonarsource.com/', seed, true)).toBe(true);
+  });
+
+  it('still excludes unrelated / look-alike domains', () => {
+    expect(URLValidationUtils.matchesDomain('https://evilsonarsource.com', seed, true)).toBe(false);
+    expect(URLValidationUtils.matchesDomain('https://sonarsource.com.attacker.net', seed, true)).toBe(false);
+    expect(URLValidationUtils.matchesDomain('https://example.com', seed, true)).toBe(false);
+  });
+
+  it('respects a co.uk registrable boundary (no cross-site bleed)', () => {
+    const ukSeed = 'https://www.example.co.uk';
+    expect(URLValidationUtils.matchesDomain('https://docs.example.co.uk/a', ukSeed, true)).toBe(true);
+    expect(URLValidationUtils.matchesDomain('https://other.co.uk/a', ukSeed, true)).toBe(false);
+  });
+
+  it('exact-host-only when includeSubdomains is false', () => {
+    expect(URLValidationUtils.matchesDomain('https://www.sonarsource.com/x', seed, false)).toBe(true);
+    expect(URLValidationUtils.matchesDomain('https://docs.sonarsource.com/x', seed, false)).toBe(false);
+  });
+});
diff --git a/src/utils/url-validation.utils.ts b/src/utils/url-validation.utils.ts
index ade4f6c..d63f640 100644
--- a/src/utils/url-validation.utils.ts
+++ b/src/utils/url-validation.utils.ts
@@ -67,7 +67,51 @@ export class URLValidationUtils {
   }
 
   /**
-   * Check if URL matches domain constraints
+   * A curated set of common two-level public suffixes. Not a full Public Suffix
+   * List (that would need a dependency + periodic updates), but it covers the
+   * cases a blind "last two labels" gets wrong — without it, `docs.a.co.uk`
+   * would reduce to `co.uk` and then match every other .co.uk site.
+   */
+  private static readonly MULTI_PART_TLDS = new Set([
+    'co.uk', 'org.uk', 'me.uk', 'ac.uk', 'gov.uk', 'net.uk', 'sch.uk', 'ltd.uk', 'plc.uk',
+    'com.au', 'net.au', 'org.au', 'edu.au', 'gov.au', 'id.au',
+    'co.nz', 'net.nz', 'org.nz', 'govt.nz', 'ac.nz',
+    'co.za', 'org.za', 'web.za', 'gov.za',
+    'co.jp', 'or.jp', 'ne.jp', 'ac.jp', 'go.jp',
+    'com.br', 'net.br', 'org.br', 'gov.br',
+    'com.cn', 'net.cn', 'org.cn', 'gov.cn',
+    'co.in', 'net.in', 'org.in', 'gen.in', 'firm.in',
+    'com.sg', 'com.hk', 'com.mx', 'com.tr', 'com.ar', 'com.tw', 'com.pl', 'com.ua',
+  ]);
+
+  /**
+   * Best-effort registrable ("base") domain — the thing a subdomain filter must
+   * key on. `www.sonarsource.com` and `docs.sonarsource.com` both -> `sonarsource.com`.
+   * IP literals and single-label hosts are returned unchanged.
+   */
+  static registrableDomain(hostname: string): string {
+    const host = (hostname || '').toLowerCase().replace(/\.$/, '');
+    // IPv4 / IPv6 literal, or a single-label host (localhost): use as-is.
+    if (/^\d+\.\d+\.\d+\.\d+$/.test(host) || host.includes(':') || !host.includes('.')) {
+      return host;
+    }
+    const labels = host.split('.');
+    if (labels.length <= 2) return host;
+    const lastTwo = labels.slice(-2).join('.');
+    if (URLValidationUtils.MULTI_PART_TLDS.has(lastTwo)) {
+      return labels.slice(-3).join('.');
+    }
+    return lastTwo;
+  }
+
+  /**
+   * Check if URL matches domain constraints.
+   *
+   * With includeSubdomains, "same domain" means the same REGISTRABLE domain — so
+   * a seed of `www.sonarsource.com` keeps `docs.`, `blog.`, `community.` etc.
+   * Previously this compared against the full seed hostname, so a `www.` seed
+   * matched only `www.sonarsource.com` and dropped every sibling subdomain — the
+   * whole point of includeSubdomains — even though discovery had found them.
    */
   static matchesDomain(url: string, baseUrl: string, includeSubdomains: boolean = true): boolean {
     try {
@@ -75,13 +119,11 @@ export class URLValidationUtils {
       const baseObj = new URL(baseUrl);
 
       if (includeSubdomains) {
-        // Allow subdomains
-        return urlObj.hostname === baseObj.hostname ||
-               urlObj.hostname.endsWith('.' + baseObj.hostname);
-      } else {
-        // Exact hostname match only
-        return urlObj.hostname === baseObj.hostname;
+        return URLValidationUtils.registrableDomain(urlObj.hostname) ===
+               URLValidationUtils.registrableDomain(baseObj.hostname);
       }
+      // Exact hostname match only.
+      return urlObj.hostname === baseObj.hostname;
     } catch (error) {
       return false;
     }