"Changing the origin does not require CloudFront to repopulate edge caches with objects from the new origin. As long as the viewer requests in your application have not changed, CloudFront will continue to serve objects that are already in an edge cache until the TTL on each object expires or until seldom-requested objects are evicted."
http://docs.aws.amazon.com/AmazonCloudFront/latest/Developer...
"Changing the origin does not require CloudFront to repopulate edge caches with objects from the new origin. As long as the viewer requests in your application have not changed, CloudFront will continue to serve objects that are already in an edge cache until the TTL on each object expires or until seldom-requested objects are evicted."