Report Security - by database

I know how to limit users that have access to a specific data folder - but what happens if a user has access to multiple folders and I want the user to see reports specific to that folder not all reports. An example is - Report 1 & Report 2

Report 1 available only in Data folder 1 

Report 2 available only in Data folder 2

Even if I have access to both folders I want the user to see only those specific to that folder