Restrict the employees available for administering ICPs based on Markets

Summary:

We had a requirement where we need to restrict the employees available for administering ICPs based on Markets (we are using Business Unit to differentiate markets).
Background : There are Functional owners who are responsible for administering ICPs to employees in a specific BU. These Functional owners are tagged to a specific BU. A functional owner belonging to Market A should not be able to find employees from Market B when they try to initiate an ICP through My Client Groups>Compensation>Administer Compensation (Functional Owners have administrator access). We tried to restrict this access through security roles, but we are still seeing employees that are part of other BUs.