//清除cookies
NSHTTPCookie *cookie;
NSHTTPCookieStorage *storage = [NSHTTPCookieStorage sharedHTTPCookieStorage];
for (cookie in [storage cookies])
{
[storage deleteCookie:cookie];
}
UIWebView清除缓存：
//清除UIWebView的缓存
[[NSURLCachesharedURLCache] removeAllCachedResponses];