Actions taken by a stored procedure are part of the Unit Of Work.
Create the stored procedure with COMMIT ON RETURN NO ( which is the default ). Then, if the calling program rolles back, all changes made by the stored procedure are rolled back, too.
If you create the stored procedure with COMMIT ON RETURN YES, the current Unit Of Work will be committed when the stored procedure returns control to the calling program.
BEGIN ATOMIC is allowed for triggers.
BEGIN NOT ATOMIC is allowed for stored procedures. ( The text string "NOT ATOMIC" may be omitted, it's the only allowed option ).