podes usar o código 301
http://www.mattcutts.com/blog/seo-advice-discussing-302-redirects/tem lá informações sobre os 301.
“That url you requested? It’s moved permanently to the new location I’m giving you.”
Helder-Oliveiras-MacBook-Pro:~ hrpoliveira$ curl -I google.pt
HTTP/1.1 301 Moved Permanently
Location:
http://www.google.pt/Content-Type: text/html; charset=UTF-8
Date: Wed, 15 Jun 2011 10:50:35 GMT
Expires: Fri, 15 Jul 2011 10:50:35 GMT
Cache-Control: public, max-age=2592000
Server: gws
Content-Length: 218
X-XSS-Protection: 1; mode=block
Helder-Oliveiras-MacBook-Pro:~ hrpoliveira$ curl google.pt
<HTML><HEAD><meta http-equiv="content-type" content="text/html;charset=utf-8">
<TITLE>301 Moved</TITLE></HEAD><BODY>
<H1>301 Moved</H1>
The document has moved
<A HREF="
http://www.google.pt/">here</A>.
</BODY></HTML>
