As you can see here, when you use string paths, rails use request's domain.
one way to tell rails that url you are passing is in another domain, is to set the protocol:
url = "http://#{another_domain_url}"
redirect_to url
If you want to use a hash, you can move path to :host
key (not tested):
redirect_to :status => :found, :host => "#{domain}#{path}"