1. A method for exchanging data between compute nodes of a computer system having a plurality of compute nodes interconnected by an inter-node communication network, each of the compute nodes having a distinct address space and a network interface interconnecting the inter-node communication network to a local packetized interconnect, the method comprising: providing a register accessible to the network interface of a sending one of the compute nodes, the register associated with a receiving one of the compute nodes; under the control of independent control logic in the network interface of the sending compute node: detecting that the register has been modified; in response to modification of the register automatically generating a local packetized interconnect packet addressed to an address specified by a value from the register in an address space of the receiving compute node corresponding to the register; encapsulating the local packetized interconnect packet, including the address, in an inter-node communication network packet; and forwarding the inter-node communication network packet to the receiving compute node by way of the inter-node communication network.