Muon spin relaxation measurements in zero magnetic field on several polycrystalline samples provide evidence that superconductivity and magnetic order do not coexist on a microscopic scale but develop inhomogeneously in Ce1+xCu2+ySi2. The distribution of magnetic and superconducting domains depends on the temperature and sensitively on variations of the stoichiometry. Superconductivity sets in first in the paramagnetic domains and, on further cooling, reduces the magnetically ordered volume fraction. However, in all samples down to T = 60 mK considerable portions remain magnetic.