Аха, да! Забыл самое важное =)
3. Использовать HTTP POST метод. POST запросы не кэшируются ни на стороне сервера, ни браузерами клиента.

Код AS3:
package {
import flash.display.Sprite;
import flash.net.URLLoader;
import flash.net.URLRequest;
import flash.net.URLRequestMethod;
public class TestCachingContent extends Sprite {
public function TestCachingContent() {
super();
// comment to test POST request
this.loadContent(URLRequestMethod.GET);
// uncomment to test POST request
//this.loadContent(URLRequestMethod.POST);
}
private function loadContent(method:String):void {
var url:String = 'http://site.ru/movie.swf';
var request:URLRequest = new URLRequest(url);
request.method = method;
if (request.method == URLRequestMethod.POST) {
request.data = 'X';
}
var loader:URLLoader = new URLLoader();
loader.load(request);
}
}
}
Лог обмена с сервером

Код:
+++GET 1+++
GET /movie.swf HTTP/1.1
x-flash-version: 9,0,124,0
If-Modified-Since: Wed, 07 Oct 2009 07:31:04 GMT
If-None-Match: "7bc1f-464ef-47553544e5e00"
User-Agent: Shockwave Flash
Host: site.ru
Connection: keep-alive
+++RESP 1+++
HTTP/1.1 304 Not Modified
Date: Thu, 08 Oct 2009 08:00:12 GMT
Server: Apache
ETag: "7bc1f-464ef-47553544e5e00"
+++GET 2+++
POST /movie.swf HTTP/1.1
x-flash-version: 9,0,124,0
Content-Type: application/x-www-form-urlencoded
Content-Length: 1
User-Agent: Shockwave Flash
Host: site.ru
Pragma: no-cache
Connection: keep-alive
Posting 1 bytes...
X
+++RESP 2+++
HTTP/1.1 200 OK
Date: Thu, 08 Oct 2009 08:00:12 GMT
Server: Apache
Last-Modified: Wed, 07 Oct 2009 07:31:04 GMT
ETag: "7bc1f-464ef-47553544e5e00"
Accept-Ranges: bytes
Content-Length: 287983
Content-Type: application/x-shockwave-flash