The scope of an agent can be based on the groups in the portal. Please navigate to Admin -> Team -> Agents -> click on edit to associate groups within the profile.
This group could be routed to a product under Admin -> Support Operations -> Multiple Products -> Edit the product -> Assign to Group and agents who specifically need to access this product could be added to that Group under Admin -> Team -> Groups. They are the ones with group access on the portal. This would restrict them to a particular product portal.