Most things are simple when you know how to do it.
In this case it was to move the Dock to a different monitor (or to restore it to your main monitor when you accidentally moved it to a secondary monitor).
TbonesTech explains it in the below video, and it is this simple:
On the monitor on which you want the Dock to appear, move the mouse to the bottom of the screen.
Then wait a moment for the Dock to move to that location.
It works in Mavericks. It might work in older versions as well, but I’ve not checked that yet.
–jeroen
via: How to Move the Dock to a External Display on a Mac – YouTube.





