This is the full answer, from IBM Technote. ND 8 has a solution. Scroll to the bottom of the page. Also, there is a utility for at least some other versions.
There are “ways” to do this. However, it depends on your current environment. For example, the servers involved (the current and new servers) are they appart of a cluster? If so, there is an easy way to do it. Make a replica on the new server, and then put the database on the current server (old server – whatever) to “out of service”. This will force users to fail over to the new one. Is that possible in your situation?
To mark a database “out of service,” follow this procedure:
1. In the Server pane of the Domino Administrator or the Web Administrator, expand All Servers or expand Clusters.
2. Select the server that contains the database you want to mark “out of service.”
3. Click the Files tab.
4. Do one of the following:
>In the Task pane in the Domino Administrator or the Web Administrator, select the folder or view that contains the database you want.
>In the Task pane in the Domino Administrator only, expand Cluster Directory (6), and then select the view you want.
5. In the Results pane, select the database or databases you want.
6. In the Tools pane, expand Database, and then click Cluster.
7. Click “Out of service,” and then click OK.