A network on chip (‘NOC’), and methods of operation of a NOC, that maintains cache coherency with invalidation messages, the NOC comprising integrated processor (‘IP’) blocks, routers, memory communications controllers, and network interface controller, each IP block adapted to a router through a memory communications controller and a network interface controller, each memory communications controller controlling communication between an IP block and memory, and each network interface controller controlling inter-IP block communications through routers, the NOC also including an invalidating module configured to send, to selected IP blocks, an invalidation message, the invalidation message representing an instruction to invalidate cached memory and the selected IP blocks, each selected IP block configured to invalidate the contents of the cached memory responsive to receiving the invalidation message.