How to disallow one domain path in robots.txt without any modules?
I don't have enough reputation to comment, so I'll just throw this out:

You can test the user agent and the URL in settings.php. Then, if it matches the crawler bot and the /path1/* criteria, you  could do a 301 Permanent Redirect for that URL within your settings.php file. Here is how:

  header('HTTP/1.0 301 Moved Permanently');
  header('Location: ' . $base_url . $redirect_path );
  exit();


where $base_url is "Twodomain" and $redirect_path is "/path1/URLfromtest"