Why the client cookie is still there and can not be removed?

I use below servlet code try to remove client cookie for log out:

LogoutServlet.java

Cookie cookies[]=request.getCookies();

    if(cookies!=null){
        for(int i=0;i<cookies.length;i++){
            if(cookies[i].getName().equals("userName")){
                cookies[i].setMaxAge(0);
                cookies[i].setPath("/");
                response.addCookie(cookies[i]);
                break;
            }
        }
    }

request.getRequestDispatcher("/login.jsp").forward(request, response);

The page jump to login.jsp I can see set-cookie in firebug(Expires is 1970 to remove cookie)

Set-Cookie  userName=abc; Expires=Thu, 01-Jan-1970 00:00:10 GMT; Path=/

But when I enter xxx/login.jsp the client cookie is still there,I can still see the cookie in the request header by firebug

Cookie  userName=abc; JSESSIONID=049034043CC3DD1231A52A534F60483B4;