PvZ Mass Mutalisk Corruptor - How to counter?

As seen in the daily 699, SoO constantly used a mass Mutalisk Corruptor force against protoss. That cannot but pose a really big question mark for me - How would I deal with it as a non-professional player? 

And there is another thing - before the Phoenix range upgrade, was this zerg strategy used as often? How would protoss deal with it then? I really don't feel that a Archon/Stalker/Sentry force would suffice, and due to the speed of the zerg air force Psi Storm would be quite inefficient.

That insane amount of multitasking is out of the question for me as a protoss player, and it seems that if I leave the zerg only one moment of breathing space, it will be a snowball from there. Constantly massing up the air units and just demolishing anything in it's path.

So, to wrap it up, here are my question to you, fellow knights, as once again I reach out to you for help:

- As a protoss, what do you do against a zerg player going for a mass Mutalisk-Corruptor force at a non professional level?

- How would protoss be able to deal with this before the Phoenix attack range upgrade was in the game and, subsequently, wahy was this zerg strategy rarely seen (I have never seen it like this, a mass Mutalisk was still quite common) when the protoss did not have the Anon Pulse-Crystals

Please lend a hand and provide some info, I am not looking forward to facing this on the ladder :D 

Thanks in advance!