How can I clear the Varnish cache?
The Cache Expiration module is designed to clear items from caches, including Varnish. 


  This module acts as a grid to detect and act upon events that will expire URLs from caches like reverse proxy caches. The Cache Expiration module is a spinoff of the expiration code of the Boost expiration code so other modules can use it. This module stands on its own and does not use Boost in any way.