fix(service-worker): clear service worker cache in safety worker

aio/content/guide/service-worker-devops.md

@@ -326,8 +326,9 @@ essentially self-destructing.
 
 Also included in the `@angular/service-worker` NPM package is a small
 script `safety-worker.js`, which when loaded will unregister itself
-from the browser. This script can be used as a last resort to get rid
-of unwanted service workers already installed on client pages.
+from the browser and remove the service worker caches. This script can
+be used as a last resort to get rid of unwanted service workers already 
+installed on client pages.
 
 It's important to note that you cannot register this worker directly,
 as old clients with cached state may not see a new `index.html` which
@@ -339,8 +340,8 @@ most sites, this means that you should serve the safety worker at the
 old Service Worker URL forever.
 
 This script can be used both to deactivate `@angular/service-worker`
-as well as any other Service Workers which might have been served in
-the past on your site.
+(and remove the corresponding caches) as well as any other Service
+Workers which might have been served in the past on your site.
 
 ### Changing your app's location
 

packages/service-worker/safety-worker.js

@@ -14,7 +14,13 @@ self.addEventListener('install', event => {
 
 self.addEventListener('activate', event => {
   event.waitUntil(self.clients.claim());
-  self.registration.unregister().then(() => {
+
+  event.waitUntil(self.registration.unregister().then(() => {
     console.log('NGSW Safety Worker - unregistered old service worker');
-  });
+  }));
+
+  event.waitUntil(caches.keys().then(cacheNames => {
+    const ngswCacheNames = cacheNames.filter(name => /^ngsw:/.test(name));
+    return Promise.all(ngswCacheNames.map(name => caches.delete(name)));
+  }));
 });