Talstar P can be used to help control cluster flies indoors and outdoors. If the cluster flies have already made their way indoors they will be harder to control because they usually hide in a wall void or other inaccessible area and are only visible when the house warms up. If the cluster flies are in an attic or drop ceiling or other dark area a fly light would do a great job controlling the population. Using small fly lights such as the Fly Web in the house would also help to catch the flies. Spray Talstar directly on baseboards, window frames, door frames, and places where utilities (pipes, wires, cables) enter in to the building and any other crack, crevice or gap where insects can enter.
Here is a link to Talstar: http://www.domyownpestcontrol.com/talstar-talstar-one-p-97.html
Link to Fly Web fly light: http://www.domyownpestcontrol.com/flyweb-fly-light-p-436.html