In the Disk Based Cache Reset section, the Force all servers in the farm to reset their disk based cache, is not available (at least, not with the May 20th rollup).
However, by looking at the code using Reflector, we can see that the checkbox does exist but, in the OnLoad event, its visibility is set to false. The good thing is that the necessary code is available in it, which is also similar to the stsadm command available at http://msdn.microsoft.com/en-us/library/aa622758.aspx, however, the stsadm command only works once. The reason is that the property value needs to be incremented each time.
You can use the following code to flush the BlobCache on all servers:
SPSite site = new SPSite(http://adventureworks);
string s = "0";
if (site.WebApplication.Properties.ContainsKey("blobcacheflushcount") && site.WebApplication.Properties["blobcacheflushcount"] != null)
s = site.WebApplication.Properties["blobcacheflushcount"] as string;
site.WebApplication.Properties["blobcacheflushcount"] = (int.Parse(s, CultureInfo.InvariantCulture) + 1).ToString(CultureInfo.InvariantCulture);
site.WebApplication.Update();
site.Dispose();