How to fix bad mirrored sculpting in zBrush

So I was happily sculpting my android girl...

 when I zoomed out and I realized that, for some reason, I had screwed the other half:

After panicking and yelling and running around the flat, I counted to ten and gave a shout to my friend David, wizard of zBrush (go, pay him a visit here: http://dgameprod.blogspot.co.uk/  ), who kindly guided me through the following method to correct the issue:

1. You have to mask the half with good geometry: 

After that, go to the lowest subdivision level of your tool, and once there, scroll down to the "Deformation" menu. There is a button called "Smart ReSym". 

Click it and voilá!

Now you have to keep scaling up on each subdivision level, and do the same.

David's note: what this button does is to create an average on both sides of your geometry, if you don't mask your good side, it will average them both and both will change. That's also the reason why it works better if you do it subdivision per subdivision instead of the latest subdivision alone. Now... texture fun!