Ruby: Updates MOESI Hammer protocol

Ruby: Updates MOESI Hammer protocol
This patch changes the manner in which data is copied from L1 to L2 cache in
the implementation of the Hammer's cache coherence protocol. Earlier, data was
copied directly from one cache entry to another. This has been broken in to
two parts. First, the data is copied from the source cache entry to a
transaction buffer entry. Then, data is copied from the transaction buffer
entry to the destination cache entry.

This has been done to maintain the invariant - at any given instant, multiple
caches under a controller are exclusive with respect to each other.