In TopLink 9.0.3, there is no API, but you could create and send your own cache coordination message. You would just need to create a change set for the object and send it.
In TopLink 11g (EclipseLink) you can use the JpaCache API evict(Class, Object, boolean) to invalidate an object in the cluster.
See,
http://wiki.eclipse.org/EclipseLink/UserGuide/JPA/Basic_JPA_Development/Caching/Cache_API
The API is also available in the native API on the IdentityMapAccessor.
FYI: TopLink 11g inlcudes EclipseLink, so migrating to EclipseLink is the same as migrating to TopLink 11g.