Myles,
Maybe leave the MTRR off until you get it working. I think that you can leave it in CAR mode until you have tested that the memory is working.
I assume you are very failiar with the FAM10 BKDG 2.6.4.1.1 DRAM and MMIO Memory Space.
Can you successfully access the memory as MMIO, F1x[BC:80] before trying F1x[1, 0][7C:40] DRAM address setup? I am not sure what will happen with a DRAM access that tries to go out a non-coherent link.
Marc