Letting one or more of your staff go? Typically, staff who have access to data may be looking for another job in the same industry or with one of your competitors. This is at least one good reason to have an exit interview process (there are many other reasons too).
Because electronic data is especially portable, you can use an exit interview to clearly communicate to your outgoing staff that your company is the sole owner of all data that the company works with on local and shared electronic media and all physical files as well. In the exit interview, it will also be important to note that your company is the sole owner of all work product produced by all company staff while they are employed by the company. Here, no ex-employee is entitled to use company data for any purpose.
This focus on data during an exit interview will also be a good opportunity to develop a checklist to cover in terms of understanding where each employee's work product may be stored (email, shored drive documents and files, local drives and even the systems of companies or customers that your company may be working with.