varnish rails devise logout configuration
===

I am using varnish in front end as caching server and apache2 with passenger is running on back-end for my rails3 application.I am using devise gem for my authentication but i am not able to lougout.

I think varnish has a option to clear logged in user session or cookie.I want to know the varnish configuration so that i can logout.

Here is my varnish configuration : 

    backend default {
    .host = "127.0.0.1";
    .port = "8080";
    }


    sub vcl_recv { 
     if(req.url ~ "my" || req.request == "POST" || req.request == "PUT" || req.request ==     "DELETE") {
    return (pass);
     }
    return (lookup);
    }
    sub vcl_fetch {

    if(req.url ~ "logout" || req.url ~ "sign_out"){
     unset beresp.http.Set-Cookie;
    }
    if (req.request == "GET") {
               unset beresp.http.Set-Cookie;
               set beresp.cacheable = true;
               set beresp.ttl = 360m;
       }

       if (req.url ~ "images/" || req.url ~ "javascripts" || req.url ~ "stylesheets"){
               set beresp.ttl = 360m;
       }
    }
