In BC Canada, many, and possibly most cities use the national police force (RCMP) as their local police force. A city that contracts out with the RCMP gets a local RCMP detachment with local headquarters, etc.

Imagine, say, Framingham Massachusetts contracting the FBI for their local police services.

I imagine that could be a big problem if the national police force suddenly had a corruption problem: many cities would also suddenly have a police corruption problem. As far as I know, that's not currently the case, although somebody might correct me.

Some BC cities, like Vancouver and Surrey, have their own police forces (Surrey is actually in the middle of phasing out RCMP usage in favour of their own police force).