How are the domains of the ACE protocol divided?

In ACE, the Transaction share domain is divided into Non-shareable, Inner, Outer, and System. Where Inner mentions that transactions in the Inner domain do not affect the Cache Line in the Outer domain.
I would like to ask the following questions:
0. Can it be understood as follows: Suppose that Core0, Core1 and Core2 share Cache Line a, where Core0-1 belongs to the Inner domain and core0-2 belongs to the Outer domain. If Core0 initiates an Invalid operation with ARDOMAIN 01 (Inner) for Cache Line a, Cache Line a in Core1 will be Invaild without affecting Core2. Is it no longer accurate that Core0's state of a is Unique?
1. Who is the divider of Inner and Outer? (CPU specification or architect?)
2. Is the division of Inner and Outer arbitrary or have special requirements? Are more than one Inner allowed in an Outer? (I saw a post saying that a Cluster is divided into Inner, so there are more than one Inner in the Outer? Is that reasonable?

Look forward to your guidance, thank you