1) invite a friend outside of instance
2) enter instance do what you need to do
3) come out of instance
4) promote friend to leader
5) leave group
6) reinvite freind, enter instance and it is reset
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This works for me 100% of the time.
Be sure your in a group with a friend and that you are the leader.
Enter the instance, do what you need to do.
Leave the instance.
Tell your buddy to disband and then have him invite you.
once he invites and you join, have him make you the leader.
Now, you can reenter the instance and it will be reset.
Wash rinse repeat