The present invention concerns a method of cleaning and/or sanitizing a separation matrix comprising multimers of immunoglobulin-binding alkali-stabilized Protein A domains covalently coupled to a porous support. The method comprises the steps of: a) optionally purifying a mixture comprising a first immunoglobulin using the separation matrix; b) providing a cleaning liquid comprising at least 50% by volume of an aqueous alkali metal hydroxide solution; and c) cleaning and/or sanitizing the separation matrix by contacting the cleaning liquid with the separation matrix for a predetermined contact time. The alkali-stabilized Protein A domains comprise mutants of a parental Fc-binding domain of Staphylococcus Protein A (SpA), as defined by SEQ ID NO 51 or SEQ ID NO 52, wherein the amino acid residues at positions 13 and 44 of SEQ ID NO 51 or 52 are asparagines and wherein at least the asparagine residue at position 3 of SEQ ID NO 51 or 52 has been mutated to an amino acid selected from the group consisting of glutamic acid, lysine, tyrosine, threonine, phenylalanine, leucine, isoleucine, tryptophan, methionine, valine, alanine, histidine and arginine.