Methods and apparatus for implementing the Intel QuickPath Interconnect® (QPI) protocol over a PCIe interface. The upper layers of the QPI protocol are implemented over a physical layer of the PCIe interface via use of QPI data bit mappings onto corresponding PCIe x16, x8, and x4 lane configurations. A QPI link layer to PCIe physical layer interface is employed to abstract the QPI link, routing, and protocol layers from the underlying PCIe physical layer (and corresponding PCIe interface circuitry), enabling QPI protocol messages to be employed over PCIe hardware. Thus, QPI functionality, such as support for coherent memory transactions, may be implemented over PCIe interface circuitry.