Freeze an 8-inch bowl. When it's cold, place the mango sorbet in the bowl and press it against the sides of the bowl. If you have a 6 1/2-inch bowl the same shape as the 8-inch bowl (such as from a set of nesting bowls), cover it with plastic wrap and press it into the sorbet to make the layer even. Freeze the sorbet for 30 minutes or until firm. Remove the 6 1/2-inch bowl.
Spread an even layer of softened raspberry sorbet on top of the mango sorbet (a 4 1/2-inch nesting bowl wrapped in plastic wrap helps with this) and freeze for another 30 minutes or until firm. Remove the 4 1/2 inch bowl.
Finally, spoon in enough softened strawberry ice cream to fill the bowl. Freeze until hard.
To unmold, dip the bowl up to the rim in warm water. Run a knife around the edge to loosen the bombe and unmold upside down onto a flat plate. You may need to run a flexible metal spatula along the edge of the bombe to release it. Freeze until ready to serve. Serve in wedges.