In one embodiment, a node for a multi-node computer system comprises a
coherence directory and a coherence controller. The coherence directory
comprises a plurality of entries, wherein each entry corresponds to a
respective coherence unit and stores a state identifying which nodes in
the computer system are storing a copy of the coherence unit and further
identifying a coherence state of the coherence unit according to a
coherence protocol implemented in the computer system. Coupled to the
directory and coupled to receive a first request for a requested
coherence unit having a first entry in the coherence directory, the
coherence controller is coupled to receive a second request for the
requested coherence unit. The coherence controller is configured to
selectively initiate coherence activity for the second request, if
coherence activity for the first request is not yet complete, dependent
on a type of the second request.