You have to get the roots of the invader out of the Zebrinus clump. If you cannot pull or tease them out, then you must dig out the clump and remove them that way. This should not effect Zebra's performance this season, especially if new growth has not yet emerged. If you do this, keep the plant watered (moist), treating it as though you have divided it.

There is a more drastic measure: systemic herbicide, but ONLY if the Zebrinus is still dormant. I do not recommend it, but it can be done carefully by "painting" the blades of the invader with the herbicide.

Perhaps I didn't read your post closely enough. Is it that you want to DETER this from happening? You may as well try to deter the weather, but if you rid the area, through regular maintenance, of unwanted (usually lawn or weed) grasses, they won't flower, seed and invade. A thick mulch in the area of the Zebrinus will help.

Actually the unwanted grass is already present in the zebra,I guess since I have already cut it down, now would be the time to dig it up and pick out as much as I can. Thanks for your help Brumeta.