BitmapImage - CheckCache public method

In file: /src/PresentationCore/System/Windows/Media/Imaging/BitmapImage.cs

I was finding everywhere but can not find public method which can tell me if BitmapImage is already in cache or not. Or is it created or not.

In my application I have listbox of images (bitmapimages) which first shows placeholder image and on download event real image.
Sometimes I need to remove that collection completely and create similar collection that contains already downloaded bitmapimages.

But on download will never be called if BitmapImage is in cache.
Is there a way to check that BitmapImage is in cache already or created successfully?