I read the answers in this question, but they still leave my question open: Does Google cache robots.txt?
I didn't find a way in the Google Webmaster Tools to invoke a re-download of my robots.txt.
Through some error, my robots.txt was replaced with:
User-agent: * Disallow: /
And now all my content was removed from Google search results.
Obviously, I'm interested in correcting this as soon as possible. I already replaced the robots.txt, but I can't find a way to make Google update the cached version.