Disable external video source on iMac?

[kjetilaa]

How do I disable the external video source from my MacBook Pro on my iMac without disconnecting the cable?
Is there a key combination on my iMac?

 

[Raima]

Shutdown normally works from memory

 

[mr.thedaniel]

Not sure if this is answering the right question, but Command+F2 switches between displaying OSX and displaying whatever is plugged into your MDP input.