IPhone : Disable/clear automatically cache in webview…

I created an app for iOS. In this app I have a webview linked with my homepage. But: there is always the same content like at the first start of the app. When I change something at my homepage or any link in it it doesn't change on my iOS device. Perhaps it is saved in cache? Notice: There is always the same content in the webview although I changed something at my homepage. I think it is the cache?!

How can I disable the cache? Or better, the cache should clear automatically, per example at start of the app.

Can anybody help me please?

Here is my code in ViewContoller.m

#import "ViewController.h"
@implementation ViewController
-(IBAction)refresh:(id)sender; {

    NSURL *url=[NSURL URLWithString: @"http://examle.com"]; NSURLRequest * requestURL=[NSURLRequest requestWithURL:url]; [_site loadRequest:requestURL];

}
- (void)viewDidLoad {

    [self refresh:self];

    NSString *path = [[NSBundle mainBundle] pathForResource:@"Plan" ofType:@"pdf"];
    NSURL *url = [NSURL fileURLWithPath:path];
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    [_ImageInWebView loadRequest:request];
    [_ImageInWebView setScalesPageToFit:YES];

    path = [[NSBundle mainBundle] pathForResource:@"Book" ofType:@"pdf"];
    url = [NSURL fileURLWithPath:path];
    request = [NSURLRequest requestWithURL:url];
    [_PDFInWebView loadRequest:request];
    [_PDFInWebView setScalesPageToFit:YES];

    [super viewDidLoad];

    _myBotton.layer.borderWidth =2.0f;
    _myBotton.layer.borderColor = [[UIColor redColor]CGColor];
}