proxy pass if not found on local

[stingreen]

Hello,
Well, the subject says it all. Is it possible ? I tried something like
the following without success. Check the htdocs first, if not found,
look under somedomain.com. 
Thanks in advance,


       location / {

            index  index.html index.htm;
            root /foo/bar/htdocs;
            proxy_pass http://somedomain.com/;
 }

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,123879,123879#msg-123879