You can choose to scan a data source at any time--even if a schedule has been set for the data source. This will execute scans for all policies to which the data source is assigned.
Select Policy Center.
Select Data sources.
Click the ellipses (…) that display when you hover at the end of the row for the data source.
Select Scan from the menu that displays.
The scan will enter the queue and execute based on its priority in the queue.