There actually shouldn't be any issue at all with the motherboard testing this. Just set a flag in the EEPROM that your testing the C6/C7 states, and try it, i

There actually shouldn't be any issue at all with the motherboard testing this. Just set a flag in the EEPROM that your testing the C6/C7 states, and try it, if the CPU exits C6/C7 with the flag set, it passed. If the system goes through a normal boot with the C6/C7 flag still set, it knows that it failed to exit C6/C7 (the supply cut out). This is basically the same procedure many motherboards use to detect if the over-clocking settings you tried were too agressive and caused the system to fail to boot.