private void registerFunctions() {
    // Register the touch partitioned region entries function if it is not already registered
    if (!isFunctionRegistered(TouchPartitionedRegionEntriesFunction.ID)) {
      registerFunctionWithFunctionService(new TouchPartitionedRegionEntriesFunction());
    }

    // Register the touch replicated region entries function if it is not already registered
    if (!isFunctionRegistered(TouchReplicatedRegionEntriesFunction.ID)) {
      registerFunctionWithFunctionService(new TouchReplicatedRegionEntriesFunction());
    }
  }
For peer-to-peer the backing cache *is* what's embedded in tomcat so it's always available

@return boolean indicating whether a backing cache is available
extensions/geode-modules/src/main/java/org/apache/geode/modules/session/catalina/PeerToPeerSessionCache.java