How to delete rows in matrix, where a value is repeated 3 times or more!

b =[ 1 1 3 6 6 6 6; 1 1 3 6 6 6 7; 1 1 3 6 6 6 8; 1 1 3 6 6 6 9;
     1 1 3 6 6 7 7; 1 1 3 6 6 7 8; 1 1 3 6 6 7 9; 1 1 3 6 6 8 8;
     1 1 3 6 6 8 9; 1 1 3 6 6 9 9; 1 1 3 6 7 7 7]
b = 11×7
     1     1     3     6     6     6     6
     1     1     3     6     6     6     7
     1     1     3     6     6     6     8
     1     1     3     6     6     6     9
     1     1     3     6     6     7     7
     1     1     3     6     6     7     8
     1     1     3     6     6     7     9
     1     1     3     6     6     8     8
     1     1     3     6     6     8     9
     1     1     3     6     6     9     9
delRow = [];
for row = 1:1:size(b,1)
    x = b(row,:);
    [~,~, counts] = unique(x);
    counts = accumarray(counts,1).';
    if (max(counts)>=3)             % if number is repeated more than twice then
        delRow = [delRow row];      % save row numbers and delete them later
    end
end
b(delRow,:)=[] % delete those row now
b = 6×7
     1     1     3     6     6     7     7
     1     1     3     6     6     7     8
     1     1     3     6     6     7     9
     1     1     3     6     6     8     8
     1     1     3     6     6     8     9
     1     1     3     6     6     9     9