{HEAD ~ bus interface} means for monitoring data moved on said system bus and for sensing via {TAIL ~ a hardware} implemented protocol any modification of said moved data for storage of validity status information in said second directory means 
{ HEAD ~ bus interface } means for monitoring data moved on said system bus and for sensing via { TAIL ~ a hardware } implemented protocol any modification of said moved data for storage of validity status information in said second directory means
HEAD HEAD HEAD HEAD HEAD HEAD OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH REL REL REL TAIL TAIL TAIL TAIL TAIL TAIL OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH OTH