Go to the Settings directory of the program, usually at C:\Program Files\jv16 PowerTools\Settings.
Open FileCache.dat with any text editor, like Notepad.
Then, set all the drives you don't wish to be cached as "false" under the CachedDrives section.
For example, if it now looks like:
c=True
d=True
You can disable the caching of the C drive by changing the text to:
c=False
d=True