Indeed, i'm using a WEBFarm for the FrontEnd Site with 2 WebServers and i have the backoffice on another Network only available to the local users and using another WebServer. They both use the same DB.
So Eric let me just clarify things here
1. The Cache Configuration used in this book doesn't fit in this scenario
2. The cache mechanism to use in this kind of scenario is the ADO.NET SQL cache dependencies
(I really like that Purge based cache mechanism..)