Purging is a command to the CDN to stop serving a file from cache.For instance, by making a purge for /images/screen.png, you instruct the network to invalidate this cached picture on all CDN servers globally .When the purge is finished and a visitor requests the purged file, the network will make a conditional request to the main server.Then the origin server will respond by delivering the newer file versions which edge serve will cache and serve to visitors.