Photoshop :: RGB To CMYK And Back To RGB Data Loss

Wondering if there is a loss of original full RGB information if changing color mode from RGB to CMYK and back to RGB.  I understand that RGB has a wider color gamut and that if changing to CMYK that I will have a narrower color gamut.  BUT, I want to know how if Adobe retains full RGB data after changing color mode to CMYK?
 
In other words, If I change from RGB to CMYK and back to RGB will I have all the original color data that I did with the original image? Does Photoshop "throw out" the full gamut information for RGB when switching to CYMK, so that when I do convert back to RGB, it is jsut looking for the comparable RGB color within the CMYK gamut now?
 
OR
 
Does Photoshop "know" the full color information regardless of in RGB or CMYK, but only changes that color information to fit within the CYMK color gamut while "remembering" what it's full color gamut WAS outside of CMYK? 
 
If I do lose full RGB info, what's the best workflow option when using for print in indesign?  Keep two seperate Photoshop files, one original RGB and one CMYK?  OR just place into InDesign as RGB and change to CMYK when exporting as PDF?