IROPS rebook policy?

This has probably been asked and answered here but I couldn't find it.

When you are cleared for upgrade on a domestic trip and get rebooked for IROPS, what is the policy on where you go?

Whenever I have done it online, it always offers me something in first if available. When the computer has automatically rebooked it, it is in first if available. But today, I do it in a SkyClub and they say they can't do it and I gotta go on the upgrade list, which I should make but I would like to know for future reference.

Is is different for domestic and international?