From: Nick Piggin <piggin@cyberone.com.au>

The crazy HASH_VALID stuff now makes no difference now.  It was there to
try to enforce no merging over a barrier, but it turned out that requests
can just be reordered.  Jens picked this up a a while ago and fixed
deadline (and I AS) by simply dispatching all reqs on the queue on
encountering a barrier.  The hash valid stuff didn't get cleaned up.