Chapters 1-2 of the Weaving High Performance Multiprocessor Fabric: Architectural Insights to the Intel QuickPath Interconnect (see mailing list for the scan)

Also there is a general book on cache coherence (much longer but will clarify details after you read the above intel book), you should have free access from the university network: A Primer on Memory Consistency and Cache Coherence Synthesis Lectures on Computer Architecture http://www.morganclaypool.com/doi/abs/10.2200/S00346ED1V01Y201104CAC016