Please note that currently we do not officially support the MSSQ based cache invalidation since this is an experimental implementation. By default Sitefinity uses webservice calls in order to invalidate the cache on the other servers. So, the server where the changes are made notifies the other servers using an http based service calls.
You may refer to the following documentation article
on how you can run Sitefinity in load balanced environment.
Do you want to have your say in the Sitefinity development roadmap? Do you want to know when a feature you requested is added or when a bug fixed? Explore the Telerik Sitefinity CMS Ideas&Feedback Portal
and vote to affect the priority of the items