I go to yoga class every Monday and Wednesday and my instructor says we are doing this stretch to cleans the "X" which can be either blood, kidneys, liver, etc.
This website says yoga has "cleansing" effects on kidneys:
Yoga instructor Tias Little recommends forward bending postures to stretch the low back region and ease the compression of your kidneys caused by too much sitting. Allowing space into the low back through forward bends allows your kidneys to work optimally and flush themselves.
Is there any evidence of "cleansing" effects on body parts from yoga or stretching?