It can be achieved by two methods, getting the domain hosted name using URL request Request.Url.Host and another by Uri.
var url = "http://www.aljazeera.com/news/2016/07/dallas-police-suspect-affiliated-group-160708132417429.html";
Uri myUri = new Uri(url);
string host = myUri.Host;
Output:
www.aljazeera.com