[Exim] Router Director condition question

I am running Exim 3.22 as a relay, and have no local users on the box.
I looked through the exim docs and was unable to find a sufficient answer...
I'm using a director and router to control delivery of messages to
spamassassin.
The router/director configs came from the documentation for spamassassin.

spamassassin:
    # do not use this router when verifying a local-part at SMTP-time
    no_verify

    # When to scan a message :
    #   -   it isn't already flagged as spam
    #   -   it isn't already scanned
    #   -   it didn't originate locally (as long as I don't harbor spammers
:-))
    condition = "${if and { {!def:h_X-Spam-Flag:} {!eq
{$received_protocol}{spam-scanned}} {!eq {$received_protocol}{local}} }
{1}{0}}"
   driver = domainlist
   search_type = partial-lsearch
   route_file = /etc/mail/mail.routes
   transport = spamassassin

My question is regarding the condition statement, and how it determines if
the message is local or not.
I want to make sure that spamassassin only scans messages being possed from
outside our network.
Internal machines should be able to relay through exim without having their
email scanned by spamassassin.
What addresses/domains are considered to be local in the condition {!eq
{$received_protocol}{local}}
Is local determined by other option settings, if so, what are they?

Owen C. Creger CCNA, CISSP
Info. Sec. Administrator
Creative Solutions, a Thomson Company.
7322 Newman Blvd.
Dexter, MI 48130
email: ocreger@???
ph: 734-426-5860 ex. 3787
fax: 734-426-5946
cell: 734-223-6270