Restarting or resetting diplay and/or GPU without logging out or rebooting?

I have a 2011 iMac 27" running Yosemite.

Is there a way to restart the monitor and/or GPU without rebooting the computer or logging off? Is there some sort of keyboard shortcut or keystroke?

I ask because sometimes my monitor freezes and displays greenish horizontal stripes. I suspect the rest of the computer is still operational (although I'm not certain of this), and I'd like to restart only the display.

Changing the resolution will reset the GPU.

I recommend the QuickRes app, since you can also set keyboard shortcuts.

Read more here http://www.macworld.com/article/2012693/mac-gems-quickres-helps-you-get-the-most-out-of-retina-displays.html