Unable to get a 304

Hi,
I am trying to reach a server and check if content has changed since last time. However I keep getting a 200 instead of 304, the second time as well.

url=URI.parse('http://www.msnbc.msn.com/js/std.js')
cd=Net::HTTP.start(url.host,url.port)
request = Net::HTTP::Get.new(url.request_uri)
response = cd.request(request)
request['HTTP_IF_NONE_MATCH']=response['Etag']
response = cd.request(request)

Should I be doing something else?
Thanks for your time.

Deepa.