persistent name

[ed at alcpress.com]

We used to have a name server, called ns1.mfin.com, that
was removed a few months ago. We modified our zone
file for the new name servers and removed ns1.mfin.com.
Yet, we still get queries for A records for the name as
well as the expected error messages in the log:

sysquery: findns error (NXDOMAIN) on ns1.mfin.com?

None of our name servers refer to the name and the
gtld-servers seem to answer correctly for the zone.
We did not then or now have an unusually high TTL.
What are the possibilities?

Ed