a reference database of libraries
a library reference database
May actually mean different things. A reference database of libraries could be a database holding library information while a library reference database could be a reference database used by the library and may be on any number of topics. I would agree with the commenters that "reference" may be a redundant word.
My local state university uses the following syntax when describing databases which would be useful for General Business topics:
Key resources for General Business
> Recommended databases to start your search
Show all General Business databases