Let's say you have an MVVM CRM application.

You have a number of customer objects in memory, through a repository.

What would be the appropriate place to handle tasks that aren't associated with traditional MVVM tasks from a GUI?

For example, let's say every few minutes you want to check to see if their address is valid and pop up a notification if it is not. Or you want to send out an hourly e-mail update. Or you want a window to pop up to remind you to call a customer at a specific time.

Where does this logic go? It's not GUI/action-oriented, and it's not logic that would be appropriate for a repository, I think.