I don't think this is possible to do from a sub directory. You are basically trying to rewrite a request sent to the root directory from within a sub directory. In order to rewrite the current url, apache should see the .htaccess file in the current directory.
However you can still redirect to the specified location, but you have to make the .htaccess file in the htdocs directory.
This is my first answer :) Not sure if this is suitable as an answer.