Hi @wburns I'm puzzled by how this works, it seems you're taking advantage of some deep L1 knowledge and I'm not familiar with it (some more comments would be helpful)

To nail one concern, it seems to me that when replacing another _sync_ you could end up having a different thread removing it via 

    l1Manager.unregisterL1WriteSynchronizer(key);

(See org.infinispan.interceptors.distribution.L1NonTxInterceptor.performL1Lookup(InvocationContext, boolean, Object, DataCommand))

Also in that same method, there is a "presentSync" check which branches in an _else_ condition where the next interceptor might not be invoked at all. Seems there is a different logic here?