Sample domain names used in Derby documentation and samples ought to conform to the recommendations of the IETF's RFC 2606, "Reserved Top Level DNS Names" (http://tools.ietf.org/html/rfc2606). RFC 2606 recommends that in documentation and examples, the domain name "example.com" should be used to refer to a hypothetical company.
The Admin Guide has several references to "sampledomain.com" that should be changed. In addition, the basic security policy shown in "Running the Network Server under the security manager" has a comment that refers to "acme.com", which should be changed too. I'm filing a separate JIRA to change the policy file itself, which is provided in demo/templates.
A few such occurrences can also be found in the Reference Manual and Developer's Guide.