Sometimes you just want to clear the entire site’s cache; if you’ve made extensive changes to many different pages for example. Doing this is relatively simple. Start by following the instructions in Clearing the caches for a specific URL in order to access the External Cache Controls. Once on the page to queue a URL for the cache, click on the “Global Settings” tab. You should see a button to “Reset External Caches”. Clicking this button will queue a request (similar to how URLs are queued in Clearing the caches for a specific URL) to wipe all the pages for your site, in both the Drupal cache and the Varnish cache.