I've just tried to replicate this problem, and have had trouble doing so...
Here's what I did:
1) Turned editing on, by clicking 'Customise this page'
2) Deleted the 'Course Overview' block
3) Added the block back- it turns up on the side like so:
4) Clicked the 'Move' icon, (little blue compass arrows) to start the move process: note the areas you can move the block to are highlighted with the dashed lines
5) Clicked the dashed lined box in the top centre of the page. The block moves to it's original position
I suppose that, to prevent this from happening in the first place, you could modify permissions relating to the blocks on the 'My Moodle' page: see http://docs.moodle.org/en/Capabilities/moodle/my:manageblocks for more details.
I realise this doesn't help with the question of how to reset a page, but it might help to prevent it from being needed to be reset in the first place