[Grocked]

Is it okay to brush/clean the forcing cone area of my 642 with a nylon brush and some light solvent like Break Free CLP?

[spwenger]

Use of the nylon-bristle brush will avoid damage to the anodized finish on the aluminum frame. However, if it's the inner surface of the forcing cone you need to clean, a Lewis or Hoppe's Lead Remover is the way to go,

[kymarkh]

Lead-away cloth works wonders on forcing cones.

[dfariswheel]

About the only way to really clean the forcing cone is to buy a Lewis Lead Remover.
This has a special cone-shaped cleaning tool that uses a brass screen to remove leading, carbon, and metal fouling from the cone.

http://www.brownells.com/aspx/NS/store/ProductDetail.aspx?p=21587&title=LEWIS%20LEAD%20REMOVER

This has the added advantage of having been used for a very good many years by revolver shooters without damaging the gun.