According to the Urban Dictionary, diggy down (or diggy diggy down) is a term referring to something that is positive or proper. e.g. The nightclub last night had an amazing atmosphere. Diggy down! http://www.urbandictionary.com/define.php?term=Diggy%20Down

In a song by INNA; named Diggy Down

It may not have been 'diggy down'. It's probably 'digging down'. Was this in writing or did you hear this somewhere? Could you clarify and also post the full sentence so we have context?