JBoss Cache currently uses eager consistency which means - when the TX ends, updates are propagated. This is necessary for fault tolerance which is after all the main reason for its existence.
However, consider the needs of a compute cluster with coarse grained parallelism (and not fault tolerance) being the objective. For this, it would be interesting if a lazy model were followed where, a lock is aquired at the start of the tx - resulting in network traffic. When the tx commits that generates no network traffic. Thus is you are iterating on a node, on a shared variable, and the other nodes sharing the variable are much slower, then no network traffic is generated.
Such things have been investigated in the past ( for example, consider Peter Keleher's work on Lazy Release consistency). It would be interesting to move the support into jboss cache given the current interest in grid computing .
Just some thoughts which I thought I could share.