Methods and apparatus for supporting dual casting of inbound system memory writes from PCIe devices to memory and a peer PCIe device. An inbound system memory write request from a first PCIe device is received at a PCIe root complex and the memory address is inspected to determine whether it falls within an address window defined for dual casting operations. If it does, an IO write request is generated from the inbound system memory write request and sent to a second PCIe device associated with the address window. During a parallel operation, the original inbound system memory write request is forwarded to a system agent configured to receive such write requests.