Ok, this has been in my mind.
First, it is a 2 fluid cooler, so the coolant side could be flushed, but oil side will not be.
With that, I haven't heard of the "oil side" plugging, but doesn't mean it doesn't.
Now, how the heck do you just flush the coolant side?
The only way I can see right now, is to hook up a hose to the "outlet" of the oil cooler only. Where the blue ( or orange ) EGR hose is. I don't think you can be sure the coolant would actually back flush the cooler by back flushing the whole system (see picture)
So, from what I see, you could back flush through "Coolant outlet" and then would go into pump and out lower radiator hose, or most would, I think.
Well, that's my take. Haven't tried it, but am thinking about it.