How can I determine whether amplification occurs from mRNA-derived cDNA or from genomic DNA contamination?

The most rigorous method to detect genomic DNA contamination, particularly with the RT² qPCR Primer Assays, is to perform a No Reverse Transcriptase (NRT) control. The PCR will have no cDNA template derived from mRNA, and any detectable product could only have been derived from genomic DNA contamination.