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Welcome to community! In the processor and PCH datasheets, its rarely mentioned root complex communication. So I would suggest you to read the book PCI Express System Architecture edited by Ravi Budruk. It expounded the Root Complex in the end of Chapter 1（page 48 to 54）.
Root complex transmits packets out of its ports and receives packets on its ports which it forwards to memory.A multi-port root complex may also route packets from one port to another port but is NOT required by the specification to do so. The chipset supports peer-to-peer packet routing between PCI Express endpoints and PCI devices, memory and graphics. It is yet to be determined if the first generation PCI Express chipsets, will support peer-to-peer packet routing between PCI Express endpoints. Remember that the specification does not require the root complex to support peer-to-peer packet routing between the multiple Links associated with the root complex.
Thanks for your answer. I've read that book (it's quite good) and the excerpt you mentioned is partly why I'm asking the question about peer-to-peer communication support in Intel's consumer root complex implementation. I haven't found much on the Internet about it which is leading me to believe that it's probably not supported, but I figure someone must know for sure!