OTS — Heuristic exception

1) The OTS specification indicates that the Resource::prepare operation
can
raise a heuristic exception. This can appears when the Resource acts as
a sub-coordinator and at least one of its resources takes a heuristic
decision.

However I didn't find a clear text explaining the behavior or
"protocol" of
a coordinator which receives such exception.
What should be the decision of this coordinator regarding to others
resource
having replied with VoteCommit?

Roll back the transaction (see 3600 above)