P1 Reads a Into Cache
•The local directory controller determines if block is locally/remotely allocated
•If remote it finds the home … by high order bits probably
•Controller asks home node for blk: No-op
•Home controller looks up directory entry for blk
•Dirty bit OFF, controller finds blk in memory, sends reply, sets xth presence bit ON
P1
a:V:4
Ctlr
a:4
01100
P2
$
Ctlr
P3
$
Ctlr
P0
a:V:4
Ctlr
Interconnection Network
In the special case that a processor references it’s own globally allocated data no communication is required, only manage the presence bits