Its not noob but it is listed on the box.  High Bandwidth Cache Controller, its just a different way of using the main graphics memory to allow faster accessing of the largest data processed by the card.   So in this case there is an option to also use main memory within that system and apparently it helps even crypto mining at least a bit.    
Best I heard the Cache described was that it used a kind of bookmark for each large section of data, if referenced that data would be called immediately by using this slip of data already contained ready and at the same time while that loads the card will also access the main memory to retreive the rest of the data.  It reduces latency possibly allows for higher minimum frame rates in a game and apparently higher hash rates for a card.  

Mining is very much about the memory bandwidth and reprocessing of the data so its a shame HBM2 did not have 4 units instead of just 2 so we could have seen how high performance could be and that would have been similar to the AMD Fury setup previously using HBM1.  I guess this might be cheaper this way