Here is example showcasing Virtuoso's support for this functionality:
<#alice> <#name> "Alice", "Alice Foo", "A. Foo" . <#alice> <#knows> <#bob>, <#carol> . <#bob> <#name> "Bob", "Bob Bar", "B. Bar" . <#carol> <#name> "Carol", "Carol Baz", "C. Baz" .
<#alice> <#name> "Alice" . <#alice> <#name> "Alice Foo" . <#alice> <#name> "A. Foo" . <#alice> <http://xmlns.com/foaf/0.1/knows> <#bob>, <#carol> . <#bob> <#name> "Bob" . <#bob> <#name> "Bob Bar" . <#bob> <#name> "B. Bar" . <#carol> <#name> "Carol" . <#carol> <#name> "Carol Baz" . <#carol> <#name> "C. Baz" .
INSERT { GRAPH <urn:sparql:tests:clear> { <#alice> <#name> "Alice" . <#alice> <#name> "Alice Foo" . <#alice> <#name> "A. Foo" . <#alice> <http://xmlns.com/foaf/0.1/knows> <#bob>, <#carol> . <#bob> <#name> "Bob" . <#bob> <#name> "Bob Bar" . <#bob> <#name> "B. Bar" . <#carol> <#name> "Carol" . <#carol> <#name> "Carol Baz" . <#carol> <#name> "C. Baz" . } }
SPARQL CLEAR GRAPH <urn:sparql:tests:clear>; Query result: callret-0 ANY Clear graph <urn:sparql:tests:clear> -- done No. of rows in result: 1