If there is communication between the isolated modules that are in different SLR regions, then one Isolated Pblock should include a Laguna PU so the routes from one SLR go to another SLR. The Laguna PU spans across two SLR regions. See the following figure.
The user must include the entire Laguna PU in one of the isolated Pblock and leave valid fence around the Laguna PU. See the following image.
In the previous figure, the blue Pblock is in SLR0 and the red Pblock is in SLR1. There is communication between the red and blue modules. The blue Pblock included two Laguna PUs, which span across the two SLR regions so that routes from SLR0 go to SLR1. In this example, the SLR boundary acts as a natural fence between the red and blue Pblocks, but there are valid fences around the two Laguna PUs in SLR1. The yellow Pblock spans across the two SLR regions and has valid fences with both red and blue Pblocks.