Method and Apparatus for Efficient Chip-To-Chip Data Transfer

Efficient data transfer between caching domains of a data processing system is achieved by a local coherency node (LCN) of a first caching domain receiving a read request for data associated with a second caching domain, from a requesting node of the first caching domain. The LCN requests the data from the second caching domain via a transfer agent. In response to receiving a cache line containing the data from the second caching domain, the transfer agent sends the cache line to the requesting node, bypassing the LCN and, optionally, sends a read-receipt indicating the state of the cache line to the LCN. The LCN updates a coherency state for the cache line in response to receiving the read-receipt from the transfer agent and a completion acknowledgement from the requesting node. Optionally, the transfer agent may send the cache line via the LCN when congestion is detected in a response channel of the data processing system.