Plpsql connecting to more than one database?

Is it possible to have a plpsql program connect to 2 databases?

This seems to imply it,
http://stackoverflow.com/questions/18257003/pl-sql-querying-a-table-on-multiple-databases

However looking at the postgresql plpsql reference,
http://www.postgresql.org/docs/current/static/plpgsql-cursors.html#PLPGSQL-CURSOR-OPENING,
doesn't seem like there is a way to specify database. Is the
stackoverflow for plpsql in some other database (not postgresql)?

Any pointers greatly appreciated.

Have users that are familiar with plpsql and have a process which needs
to be done withing transactions in 2 databases.
begin in db1
begin in db2

work on 1
work on 2

if work on both dbs worked

commit db1
commit db2

Do they need to use some other language (Java/Python)? How about a
foreign data wrapper?