as Ady already said, currently only MSMQ is supported as the delivery mechanism for the eviction messages that OpenAccess sends. Our second level cache is populated only by the local read requests, but entries in it can be evicted both locally and from remote cache participants. The eviction uses reliable multicasting provided via MSMQ, and yes, it is asynchronous. The big advantage of this approach is that the caches are populated by local requests, so different nodes will have different entries, and that the access to the caches is really fast, not involving any serialization or network latency. Also, the eviction messages are comparativly small in size and are efficiently broadcasted to all interested parties.
For farms of servers that use the same cache cluster it is a good decision to tune the load balancers so that work units do not hop between servers to much in order to avoid potential issues coming from the asynchronous nature of the eviction messaging.
the Telerik team