The interagency here just means getting together the DoD, the White House, the BBG, USAID, CIA, etc to coordinate messaging so that they are all giving the same

The interagency here just means getting together the DoD, the White House, the BBG, USAID, CIA, etc to coordinate messaging so that they are all giving the same story. Actually, the interagency is a catchall term to mean communication between different parts of the executive branch, as they otherwise report up to different Secretaries and command structures. There are a number of different manners and ways that interagency coordination and collaboration is done and it is not specific to public messaging.