I'm wondering if there is a specific CLI command I can send to a Control4 Master Controller that will instruct it to run a Media Scan. 

I use a linux machine to transcode and organize all of my Control4 music, and I would like to automate it to the point where I don't have to log into composer and run the scan every time I add something new. 

Any I know I can have it scan every night, but usually when I download an album, I want to listen to it right away.

Any way to achieve this within composer would be helpful as well, it doesn't have to be CLI, just figure that's the easiest way for the two linux machines to communicate. 

You can create a custom button (or experience button) which does a scan. 

The action for that is found under the respective Network Storage driver, USB stick/HDD driver if plugged into a controller or the controller itself if it's an older device with built-in storage.