This answer is heavily influenced by a conversation here: http://www.tek-tips.com/viewthread.cfm?qid=1395151&page=3
ALTER SYSTEM ENABLE RESTRICTED SESSION;
begin
for x in (
select Sid, Serial#, machine, program
from v$session
where
machine <> 'MyDatabaseServerName'
) loop
execute immediate 'Alter System Kill Session '''|| x.Sid
|| ',' || x.Serial# || ''' IMMEDIATE';
end loop;
end;
I skip killing sessions originating on the database server to avoid killing off Oracle's connections to itself.