Asana has a general solution for this scenario, called Divisions.
It’s quite a complex topic as it can be configured in a number of ways and carries with it a number of resulting behaviors. You can read about it here:
It can only be set up by Asana Sales, not on the customer admin side, so you should contact them for a full discussion of it; they will help you decide if it’s appropriate and how they should set it up in your particular case.