{HEAD ~ All requests} for a cache line are screened by {TAIL ~ the blocker} associated with each home directory 
are screened by
{ HEAD ~ All requests } for a cache line are screened by { TAIL ~ the blocker } associated with each home directory
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH