Which MARC record field identifies the originating server?

Hi,
 
I have been downloading MARC records asynchronously from multiple Z39.50
servers using Net::Z3950::ZOOM. I push them into an array as they arrive.
When I later examine the records, I'd like to be able to identify which
library server each record came from. 
 
Does every MARC record contain a field/subfield that identifies the library
the record came from? Field 040 seems only to identify the organization that
originally created the record, which may be different from the library whose
server I downloaded the record from. If there is no such field for every
record, I'll have to tag the records as they come in, but I suspect this
will slow down the downloading process.
 
Many thanks!

- Chris Morgan