Hi Zafer -
Many customers use use Priority groups in the pool to use remote servers as the "pool of last resort".
If you always want the local server(s) to be used, you can use the following configuration:
1) Put both local and remote servers in the pool in each data center, assigning the local server(s) higher priority
2) Add a monitor to the pool and verify all servers can be successfully monitored
3) Configure SNATs as necessary to force response traffic back to LTM when LB to the remote servers.
HTH
/deb