Hi,
Honestly it depends how your Business units are setup. If you are trying to track different locations for example sales from two different Business Units then you would build the audiences according to the Business Units locations.
BU = Business Unit
BU Location 1 & BU Location 2 will need to be different locations, from there you will need two campaigns and two audiences. Then it is through audiences that you would select the BU's that you are trying to select.
Let me know if this helps, otherwise contacting your CSM would be the best to gain a better understanding on this.
